Minimum Equipment List (MEL)
--Fall 2012--NATA Aircraft Maintenance & System Technology CommitteeBest PracticesMinimum Equipment List (MEL)The Minimum Equipment List (MEL) is a document and method aircraft operators use to obtainrelief from Federal Aviation Regulations requiring that all equipment installed on the aircraft beoperative at the time of flight. It is aircraft-specific and spells out which pieces of equipmentmay be allowed to be inoperable along with any procedures that are required for an aircraft tooperate under specific conditions while maintaining airworthiness.The MEL is developed from the Master Minimum Equipment List (MMEL), which is producedby the aircraft manufacturer and approved during certification of the airplane. The MMEL isused by individual operators to develop their MEL and takes into consideration an operator’smore particular equipment, instrument and operational conditions. Operator MELs foradministrative control may include items not contained in the MMEL; however, the FederalAviation Administration (FAA) must approve the administrative control items. An operator’sMEL may differ in format from the MMEL, but cannot be less restrictive than the MMEL. Whenthe individual operator’s MEL is approved and authorized, it then becomes a SupplementalType Certificate (STC), and permits operation of the aircraft with inoperative equipment.The FAA has MMELs for most of the type-certificated aircraft in use today. These MMELs canbe found on the FAA’s Flight Standards Information Management System (FSIMS) under thePublications, or by going to http://fsims.faa.gov/PublicationForm.aspxThere is also an MMEL Industry/FAA Group designed to assist the FAA in the development ofMMEL policy and revisions. The goal of the group is to harmonize and gain consensus onMMEL issues, capitalize on the expertise of the aviation industry, and reduce the FAA’sworkload in the development of MMEL policy and revisions.BackgroundThe MEL concept originally applied to air carriers, commercial operators and those generalaviation operators of multi-engine aircraft for which the FAA had developed an MMEL.Operators of aircraft for which the FAA had not developed an MMEL had to ensure that allNATA Aircraft Maintenance & System Technology Committee Best Practices – MELPage 1of 5
aircraft discrepancies occurring during the normal operation of the aircraft were repaired beforethe aircraft could be operated again. This meant that all the aircraft’s instruments andequipment, regardless of whether they were essential or not to the flight operation, had to beoperative. The regulation placed a huge burden on many aircraft operators and put them atrisk of being out of compliance.In 1989, the FAA revised the regulations to those we have today; operators can fly their aircraftwith inoperative instruments and equipment, under a framework of a controlled maintenanceand inspection program, including repairs and parts replacement.Regulatory RequirementTitle 14 CFR section 91.205 lists the aircraft equipment and instruments that must be installedand requires the instruments and equipment to be in an operable condition. Part 91, section91.213, addresses inoperative equipment and provides relief from section 91.205 through the useof an FAA-approved MEL. It allows for the operation of aircraft with instruments andequipment in an inoperable condition. The regulation also provides a list of instruments andequipment that may not be included in an MEL. For example, instruments and equipment thatare either specifically or otherwise required by the airworthiness standards under which theaircraft is type certificated and which are essential for safe operations under all operatingconditions, or instruments and equipment required by an airworthiness directive to beinoperable, unless the airworthiness directive provides otherwise, may not be included in anMEL.MEL Operations and Maintenance ProceduresAn MEL is intended to permit operation with inoperative instruments or equipment for aperiod of time until repairs can be accomplished – it is not a “free pass.” Repairs must beaccomplished at the earliest opportunity.To maintain an acceptable level of safety and reliability, the MEL establishes limitations on theduration of and conditions for operation with inoperative equipment. When inoperativeequipment is discovered, the regulations require that it be reported via proper entry in theaircraft maintenance record/logbook. The item is then repaired, or deferred for repair butdeactivated and placarded by an appropriately certificated maintenance person (per 43.7) perthe MEL or other approved means acceptable to the FAA, prior to further operation.MEL conditions and limitations do not relieve the operator from determining that the aircraft isin condition for safe operation with items of equipment inoperative, and the deactivation of oneinoperative system should not reduce the performance of any other instruments or equipment.NATA Aircraft Maintenance & System Technology Committee Best Practices – MELPage 2 of 6
“(O)” and “(M)” procedures must contain descriptions of the individual steps necessary toaccomplish each operation or maintenance function. For example, if the MMEL contains an“(M)” symbol with a provision that a valve must be closed, the operator must include theappropriate maintenance procedures to close the valve as part of the operator’s manual or MEL.The “(O)” symbol indicates a requirement for a specific operations procedure that must beaccomplished in planning for and/or operating with the listed item inoperative. Normally, theflight crew accomplishes these procedures; however, other personnel may be qualified andauthorized to perform the functions. The satisfactory accomplishment of all procedures,regardless of who performs them, is the responsibility of the operator. Appropriate proceduresare required to be published as a part of the operator’s manual or MEL.The “(M)” symbol indicates a requirement for a specific maintenance procedure, which must beaccomplished prior to operation with the listed item inoperative. Normally, maintenancepersonnel accomplish these procedures; however, other personnel may be qualified andauthorized. Procedures requiring specialized knowledge or skill, or requiring the use of tools ortest equipment should be accomplished by maintenance personnel. Like the “(O)” procedures,the satisfactory accomplishment of all maintenance procedures, regardless of who performsthem, is the responsibility of the operator. The appropriate procedures are required to bepublished as part of the operator’s manual or MEL as well.The “Remarks and Exceptions” section of the MMEL generally contains provisos that includespecific conditions under which an item of equipment may be inoperative. These provisos mustbe carried over either verbatim into the operator’s MEL or by using equivalent terminology.Provisos are distinct from “(O)” and “(M)” procedures. A procedure is an action that must beperformed. A proviso is a condition that must exist (for example, a proviso that operationsmust be conducted under VFR, an operation under an IFR flight plan is not permitted,regardless of the weather conditions).Where the MMEL states “as required by 14 CFR,” the procedures document should list theparticular regulation by part and section or describe the actual 14 CFR requirement applicableto the operator’s particular operation (for example, where the regulation requires a clock for IFRflight, the operator’s procedures document should say “May be inoperative for VFR).If the “(O)” and “(M)” procedures are already stated in the AFM, the maintenancemanual, or other available FAA-approved source, the operator needs only to show thereference. If the operator uses this reference format in the procedures document, thereferenced source must be readily available to the ground support personnel and a copyof the references source must be carried in the aircraft and be readily available to theflight crew.NATA Aircraft Maintenance & System Technology Committee Best Practices – MELPage 3 of 6
If “(O)” and “(M)” procedures are not in the AFM, maintenance manual, or otheravailable FAA-approved source, or if the operator wishes to use a different procedure,the operator must list the procedure in the procedures document.The procedures document may not conflict with AFM limitations, emergency procedures, ADs,or the aircraft maintenance manual.Repair IntervalsThe repair interval categories (A, B, C, and D) listed in column 1 of the MMEL apply only tooperations conducted under Parts 121, 125, 129, and 135.All users of an MEL approved under Parts 91K, 121, 125, 129, and 135 must effect repairs ofinoperative systems or components, deferred in accordance with the MEL, at or prior to therepair times established by the following letter designators:Category A. This category item must be repaired within the time interval specified in theremarks column of the certificate holder’s approved MEL.Category B. This category item must be repaired within 3 consecutive calendar-days (72 hours),excluding the day the malfunction was recorded in the aircraft maintenance record/logbook.For example, if it were recorded at 10 a.m. on January 26, the 3-day interval would begin atmidnight on January 26 and end at midnight on January 29.Category C. This category item must be repaired within 10 consecutive calendar-days (240hours), excluding the day the malfunction was recorded in the aircraft maintenancerecord/logbook. For example, if it were recorded at 10 a.m. on January 26, the 10-day intervalwould begin at midnight on January 26 and end at midnight on February 5.Category D. This category item must be repaired within 120 consecutive calendar-days (2880hours), excluding the day the malfunction was recorded in the aircraft maintenance log and/orrecord.The FAA does have policy in Order 8900.1 to allow continuing authorizations (extensions). Thepolicy, states that if a certificate holder or program manager has the authorization to use anFAA-approved MEL they also have the authority to use a continuing authorization to approve asingle extension to the repair interval for category B or C items (3 days and 10 daysrespectively). The certificate holder/program manager needs to notify the responsible FAA fieldoffice within 24 hours of the use of the extension authority. This authorization is good for a onetime extension. If the operator wants or needs to extend the interval again, the operator mustget approval from the FAA office. A certificate holder/program manager is not authorized toextend the maximum repair time for category A and D items, as specified in the approved MEL.NATA Aircraft Maintenance & System Technology Committee Best Practices – MELPage 4 of 6
MEL Approval ProcessWhether you are a Part 91 operator or a commercial operator, an FAA operations inspector, or inthe case of a commercial operator, the principal operations inspector (POI) assigned to thecertificate, will be the primary FAA official responsible for the overall process of evaluating, andapproving an MEL document. The POI or operations inspector works with the correspondingprincipal maintenance and principal avionics inspector to complete the review and approval ofthe MEL. The principal maintenance inspector is responsible to evaluate and approve acertificate holder’s MEL Management Program as prescribed in operations specification(OpSpec)/management specification (MSpec) D095, Minimum Equipment List (MEL)Authorization. If you are a Part 91 operator, the same FAA personnel are involved; however,the outcome is the issuance of a Letter of Authorization (LOA) instead of operationspecifications.In either case, the operator must develop and submit to the FAA the Operations (O) andMaintenance (M) procedures using guidance contained in the manufacturer’s aircraft flight andmaintenance manuals, the manufacturer’s recommendations, engineering specifications.The POI will begin the review of the MEL package when he or she finds the proposed MEL tobe complete and to contain the required information. This is usually where the issues can beginfor an operator. Even though the inspector should compare the MEL to the MMEL, the reviewor analysis process can be frustrating and challenging. Usually, the issues surround the “(O)”and “(M)” procedures, the length of time allowed for deferral, or the parts management portionof the MEL management program. Secondly, even though the FAA guidance tells the inspectorthat he or she should conduct a timely review there can be delays. There have been complaintsby operators in the industry that MELs can remain in an FAA office up to a year without anyaction. Of course, it is a two-way street. The operator should also be responsive and not let theMEL linger in their office.If an operator finds themselves in a situation where the review is taking too long, or no action isbeing taken at all, there is the option of elevating the issue to the supervisor or manager.Unfortunately, there is no standard answer on how to proceed; it usually depends on therelationship between the operator and the FAA office. MEL development is not for the weak ofheart. The operator should make sure it has the experience on hand to manage the process.After the POI completes the final review and is satisfied that the MEL meets the applicablerequirements, the POI will sign the MEL control page or the individual MEL pages to signifyapproval and the PMI will issue OpSpec/MSpec D095.Part 91 operators, who apply to the FAA for an MEL, will receive an LOA that authorizes theuse of the MEL and is specific to the aircraft make, model, serial number and registrationNATA Aircraft Maintenance & System Technology Committee Best Practices – MELPage 5 of 6
number.MELs and LOAs are not transferrable with the sale of an aircraft. If an operator sells an airplanewith an MEL or LOA, the documents should be returned to the FSDO. If an operator changeslocations and moves out of one FAA district office jurisdiction to another or even to a differentpart of the country, the operator needs to notify both of the FAA offices. The previous officeshould forward the MEL file to the new FAA office. Again, this is where industry hascomplained that an inspector in the new office will require that the operator resubmit its MELfor approval. However, that is neither what the regulations nor the inspector guidance states,and in those situations the operator may want to raise his concerns.FAA Order 8900.1 Volume 4 Chapter 4 section 7 MEL Approval Process for 14 CFR 91K,121, 135, and 129 Operators and AC 91-67 MINIMUM EQUIPMENT REQUIREMENTSFOR GENERAL AVIATION OPERATIONS Date: 6/28/91, contains detailed informationabout the MEL submission, review and approval process.NATA Aircraft Maintenance & System Technology Committee Best Practices – MELPage 6 of 6
The MEL is developed from the Master Minimum Equipment List (MMEL), which is produced by the aircraft manufacturer and approved during certification of the airplane. The MMEL is used by individual operators to develop their MEL and takes into consideration an operator’s more particular equipment, instrument and operational conditions.File Size: 403KBPage Count: 6
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